Showing papers by "University of Duisburg-Essen published in 2004"

HDL induces NO-dependent vasorelaxation via the lysophospholipid receptor S1P3

Abstract: HDL is a major atheroprotective factor, but the mechanisms underlying this effect are still obscure. HDL binding to scavenger receptor-BI has been shown to activate eNOS, although the responsible HDL entities and signaling pathways have remained enigmatic. Here we show that HDL stimulates NO release in human endothelial cells and induces vasodilation in isolated aortae via intracellular Ca2+ mobilization and Akt-mediated eNOS phosphorylation. The vasoactive effects of HDL could be mimicked by three lysophospholipids present in HDL: sphingosylphosphorylcholine (SPC), sphingosine-1-phosphate (S1P), and lysosulfatide (LSF). All three elevated intracellular Ca2+ concentration and activated Akt and eNOS, which resulted in NO release and vasodilation. Deficiency of the lysophospholipid receptor S1P3 (also known as LPB3 and EDG3) abolished the vasodilatory effects of SPC, S1P, and LSF and reduced the effect of HDL by approximately 60%. In endothelial cells from S1P3-deficient mice, Akt phosphorylation and Ca2+ increase in response to HDL and lysophospholipids were severely reduced. In vivo, intra-arterial administration of HDL or lysophospholipids lowered mean arterial blood pressure in rats. In conclusion, we identify HDL as a carrier of bioactive lysophospholipids that regulate vascular tone via S1P3-mediated NO release. This mechanism may contribute to the vasoactive effect of HDL and represent a novel aspect of its antiatherogenic function.

Prospective, Randomized, Multicenter, Controlled Trial of a Bioartificial Liver in Treating Acute Liver Failure

Abstract: Objective: The HepatAssist liver support system is an extracorpo-real porcine hepatocyte-based bioartificial liver (BAL). The safety and efficacy of the BAL were evaluated in a prospective. random-ized, controlled, multicenter trial in patients with severe acute liver failure. Summary Background Data: In experimental animals with acute liver failure, we demonstrated beneficial effects of the BAL. Similarly, Phase I trials of the BAL in acute liver failure patients yielded promising results. Methods: A total of 171 patients (86 control and 85 BAL) were enrolled. Patients with fulminant/subfulminant hepatic failure and primary nonfunction following liver transplantation were included. Data were analyzed with and without accounting for the following confounding factors: liver transplantation, time to transplant, disease etiology, disease severity, and treatment site. Results: For the entire patient population, survival at 30 days was 71% for BAL versus 62% for control (P = 0.26). After exclusion of primary nonfunction patients, survival was 73% for BAL Versus 59% for control (it = 147; P= 0.12). When Survival was analyzed accounting for confounding factors. in the entire patient Population, there was no difference between the 2 groups (risk ratio = 0.67; P = 0.13). However, survival in fulminant/subfulminant hepatic failure patients was significantly higher in the BAL compared with the control group (risk ratio 0.56: P = 0.048). Conclusions: This is the first prospective, randomized, controlled trial of an extracorporeal liver support system, demonstrating safety and improved survival in patients with fulminant/subfulminant hepatic failure.

G protein-coupled receptor-dependent development of human frontal cortex.

Abstract: The mammalian cerebral cortex is characterized by complex patterns of anatomical and functional areas that differ markedly between species, but the molecular basis for this functional subdivision is largely unknown. Here, we show that mutations in GPR56, which encodes an orphan G protein-coupled receptor (GPCR) with a large extracellular domain, cause a human brain cortical malformation called bilateral frontoparietal polymicrogyria (BFPP). BFPP is characterized by disorganized cortical lamination that is most severe in frontal cortex. Our data suggest that GPCR signaling plays an essential role in regional development of human cerebral cortex.

Overview and application of the AQEM assessment system

Abstract: The main objective of the European Union (EU) funded project AQEM1 was to develop a framework of an assessment system for streams in Europe based on benthic macroinvertebrates that fulfils the requirements of the EU Water Framework Directive. Initial assessment methods for 28 European stream types and more generally applicable tools for stream biomonitoring in Europe were generated.

Glial Tumor Grading and Outcome Prediction Using Dynamic Spin-Echo MR Susceptibility Mapping Compared with Conventional Contrast-Enhanced MR: Confounding Effect of Elevated rCBV of Oligodendroglimoas

Abstract: BACKGROUND AND PURPOSE: The MR imaging characteristics of oligodendrogliomas and astrocytomas on spin-echo (SE), echo-planar relative cerebral blood volume (rCBV) maps, to our knowledge, have not previously been emphasized. We compared the specificity of SE rCBV mapping with that of conventional, contrast material–enhanced MR imaging in differentiating high- from low-grade glial tumors and in predicting survival of patients with these lesions. METHODS: Thirty consecutive adult patients with suspected gliomas underwent conventional and rCBV MR imaging. Representative maximal rCBV regions of interest were chosen from each lesion. Resultant values were normalized to those of corresponding, contralateral, uninvolved regions. These normalized CBV (nCBV) values were correlated with degree of contrast enhancement, histopathologic tumor grade, and survival. RESULTS: Twenty-two patients had astroctyomas and eight had oligodendrogliomas. With an nCBV cutoff ratio of 1.5, 13 of 13 high-grade astrocytomas were correctly categorized, three of which did not enhance. Seven of nine low-grade astrocytomas were correctly classified by their nCBV values, including one enhancing lesion. Of eight oligodendrogliomas, four of four high-grade and two of four low-grade tumors had elevated nCBV values; two low-grade oligodendrogliomas enhanced, one with nCBV greater than 1.5 and one with nCBV less than 1.5. In 19 patients with astrocytoma for whom survival data were available, correlation with survival was better for nCBV (mean survival 91 ± 14 months for nCBV 1.5, P P = .03). CONCLUSION: Elevated SE rCBV was a sensitive, but not specific, marker for high-grade histopathology: all high-grade tumors had nCBV foci values greater than 1.5. No tumor with nCBV region of interest less than 1.5 was high grade (100% predictive value for excluding high grade). Degree of nCBV elevation was a stronger predictor of both tumor grade and survival than was degree of enhancement. A significant proportion of low-grade glial neoplasms, most notably oligodendrogliomas, may display high rCBV foci not reflective of high-grade histopathology.

First-principles calculation of the structure and magnetic phases of hematite

Abstract: Rhombohedral $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ has been studied by using density-functional theory (DFT) and the generalized gradient approximation (GGA). For the chosen supercell all possible magnetic configurations have been taken into account. We find an antiferromagnetic ground state at the experimental volume. This state is 388 meV/(Fe atom) below the ferromagnetic solution. For the magnetic moments of the iron atoms we obtain $3.4{\ensuremath{\mu}}_{\mathrm{B}},$ which is about $1.5{\ensuremath{\mu}}_{\mathrm{B}}$ below the experimentally observed value. The insulating nature of $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ is reproduced, with a band gap of 0.32 eV, compared to an experimental value of about 2.0 eV. Analysis of the density of states confirms the strong hybridization between Fe $3d$ and O $2p$ states in $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}.$ When we consider lower volumes, we observe a transition to a metallic, ferromagnetic low-spin phase, together with a structural transition at a pressure of 14 GPa, which is not seen in experiment. In order to take into account the strong on-site Coulomb interaction U present in ${\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ we also performed $\mathrm{D}\mathrm{F}\mathrm{T}+U$ calculations. We find that with increasing U the size of the band gap and the magnetic moments increase, while other quantities such as equilibrium volume and Fe-Fe distances do not show a monotonic behavior. The transition observed in the GGA calculations is shifted to higher pressures and eventually vanishes for high values of U. Best overall agreement, also with respect to experimental photoemission and inverse photoemission spectra of hematite, is achieved for $U=4\mathrm{eV}.$ The strength of the on-site interactions is sufficient to change the character of the gap from $d\ensuremath{-}d$ to $\mathrm{O}\ensuremath{-}p\ensuremath{-}\mathrm{Fe}\ensuremath{-}d.$

Mechanisms of DNA double strand break repair and chromosome aberration formation.

Abstract: It is widely accepted that unrepaired or misrepaired DNA double strand breaks (DSBs) lead to the formation of chromosome aberrations. DSBs induced in the DNA of higher eukaryotes by endogenous processes or exogenous agents can in principle be repaired either by non-homologous endjoining (NHEJ), or homology directed repair (HDR). The basis on which the selection of the DSB repair pathway is made remains unknown but may depend on the inducing agent, or process. Evaluation of the relative contribution of NHEJ and HDR specifically to the repair of ionizing radiation (IR) induced DSBs is important for our understanding of the mechanisms leading to chromosome aberration formation. Here, we review recent work from our laboratories contributing to this line of inquiry. Analysis of DSB rejoining in irradiated cells using pulsed-field gel electrophoresis reveals a fast component operating with half times of 10-30 min. This component of DSB rejoining is severely compromised in cells with mutations in DNA-PKcs, Ku, DNA ligase IV, or XRCC4, as well as after chemical inhibition of DNA-PK, indicating that it reflects classical NHEJ; we termed this form of DSB rejoining D-NHEJ to signify its dependence on DNA-PK. Although chemical inhibition, or mutation, in any of these factors delays processing, cells ultimately remove the majority of DSBs using an alternative pathway operating with slower kinetics (half time 2-10 h). This alternative, slow pathway of DSB rejoining remains unaffected in mutants deficient in several genes of the RAD52 epistasis group, suggesting that it may not reflect HDR. We proposed that it reflects an alternative form of NHEJ that operates as a backup (B-NHEJ) to the DNA-PK-dependent (D-NHEJ) pathway. Biochemical studies confirm the presence in cell extracts of DNA end joining activities operating in the absence of DNA-PK and indicate the dominant role for D-NHEJ, when active. These observations in aggregate suggest that NHEJ, operating via two complementary pathways, B-NHEJ and D-NHEJ, is the main mechanism through which IR-induced DSBs are removed from the DNA of higher eukaryotes. HDR is considered to either act on a small fraction of IR induced DSBs, or to engage in the repair process at a step after the initial end joining. We propose that high speed D-NHEJ is an evolutionary development in higher eukaryotes orchestrated around the newly evolved DNA-PKcs and pre-existing factors. It achieves within a few minutes restoration of chromosome integrity through an optimized synapsis mechanism operating by a sequence of protein-protein interactions in the context of chromatin and the nuclear matrix. As a consequence D-NHEJ mostly joins the correct DNA ends and suppresses the formation of chromosome aberrations, albeit, without ensuring restoration of DNA sequence around the break. B-NHEJ is likely to be an evolutionarily older pathway with less optimized synapsis mechanisms that rejoins DNA ends with kinetics of several hours. The slow kinetics and suboptimal synapsis mechanisms of B-NHEJ allow more time for exchanges through the joining of incorrect ends and cause the formation of chromosome aberrations in wild type and D-NHEJ mutant cells.

Do psychosocial variables predict weight loss or mental health after obesity surgery? A systematic review.

Abstract: HERPERTZ, S., R. KIELMANN, A.M. WOLF, J. HEBEBRAND, AND W. SENF. Do psychosocial variables predict weight loss or mental health after obesity surgery? A systematic review. Obes Res. 2004;12:1554–1569. Objective: The objective of this study was to present a systematic review of psychological and psychosocial predictors of weight loss and mental health after bariatric surgery. This systematic review included all controlled and noncontrolled trials of the last 2 decades with either a retrospective or prospective design and a follow-up period of at least 1 year. Research Methods and Procedures: The relevant literature was identified by a search of computerized databases. All articles published in English and German between 1980 and 2002 were reviewed. Results: Using the above inclusion/exclusion criteria, 29 articles were identified focusing on psychosocial predictors of weight loss and mental health after obesity surgery. Discussion: Personality traits have no predictive value for the postoperative course of weight or mental state. Apart from serious psychiatric disorders including personality disorders, psychiatric comorbidity seems to be of more predictive value for mental and physical well-being as two essential aspects of quality of life than for weight loss postsurgery. However, depressive and anxiety symptoms as correlates of psychological stress with regard to obesity seem to be positive predictors of weight loss postsurgery. The severity of the symptoms or the disorder is more relevant for the outcome of obesity surgery than the specificity of the symptoms. It is also not solely the consumption of distinct “forbidden” foods, such as sweets or soft drinks, but rather a general hypercaloric eating behavior, either as an expression of the patient’s inadequate compliance or a dysregulation in energy balance, which is associated with a poor weight loss postsurgery.

Prognostic Value of Tubular Proteinuria and Enzymuria in Nonoliguric Acute Tubular Necrosis

Abstract: Background: Acute tubular necrosis (ATN) has high mortality, especially in patients who require renal replacement therapy (RRT). We prospectively studied the diagnostic accuracy of the urinary excretion of low-molecular-weight proteins and enzymes as predictors of a need for RRT in ATN. Methods: In 73 consecutive patients with initially nonoliguric ATN, we measured urinary excretion of α1- and β2-microglobulin, cystatin C, retinol-binding protein, α-glutathione S -transferase, γ-glutamyltransferase, lactate dehydrogenase, and N -acetyl-β-d-glucosaminidase early in the course of ATN. Results: Twenty-six patients (36%) required RRT a median of 4 (interquartile range, 2–6) days after detection of proteinuria and enzymuria. Patients who required RRT had higher urinary cystatin C and α1-microglobulin [median (interquartile range), 1.7 (1.2–4.1) and 34.5 (26.6–45.1) g/mol of creatinine] than patients who did not require RRT [0.1 (0.02–0.5) and 8.0 (5.0–17.5) g/mol of creatinine]. Urinary excretion of cystatin C and α1-microglobulin had the highest diagnostic accuracies in identifying patients requiring RRT as indicated by the largest areas under the ROC curves: 0.92 (95% confidence interval, 0.86–0.96) and 0.86 (0.78–0.92), respectively. Sensitivity and specificity were 92% (95% confidence interval, 83–96%) and 83% (73–90%), respectively, for urinary cystatin C >1 g/mol of creatinine, and 88% (78–93%) and 81% (70–88%) for urinary α1-microglobulin >20 g/mol of creatinine. Conclusion: In nonoliguric ATN, increased urinary excretion of cystatin C and α1-microglobulin may predict an unfavorable outcome, as reflected by the requirement for RRT.

Timescales in the response of materials to femtosecond laser excitation

Abstract: The interaction of ultrashort laser pulses with materials involves a number of special features that are different from laser–matter interaction for longer pulse durations. For femtosecond laser excitation the fundamental physical processes such as energy deposition, melting, and ablation are separated in time. By choosing proper time windows, the various processes can be investigated separately. We present selected examples of theoretical studies of free electron excitation in metals, timescales of different melting processes, and peculiarities of near-threshold ablation. Depending on the timescales and intensity ranges, the discussed processes are combined in an overall picture of possible pathways of the material from excitation to ablation.

Unified Model for the Free-Electron Avalanche in Laser-Irradiated Dielectrics

Abstract: We develop a model describing the free-electron generation in transparent solids under high-intensity laser irradiation. The multiple rate equation model unifies key points of detailed kinetic approaches and simple rate equations to a widely applicable description, valid on a broad range of time scales. It follows the nonstationary energy distribution of electrons on ultrashort time scales as well as the transition to the asymptotic avalanche regime for longer irradiations. The role of photoionization and impact ionization is clarified in dependence on laser pulse duration and intensity.

Organophosphate flame retardants and plasticisers in wastewater treatment plants

Abstract: Previous studies have revealed that chlorinated and non-chlorinated organophosphorous flame retardants and plasticisers are important contaminants in German surface waters and it has been demonstrated that wastewater treatment plants contribute to the emission of these substances. In this study temporal development as well as elimination efficiency were determined in two wastewater treatment plants (STP) in the Ruhr/Rhine area at different stages of the wastewater treatment process. The samples were analysed for the non-chlorinated organophosphate esters tri-n-butylphosphate (TnBP), tri-iso-butylphosphate (TiBP), tris-(butoxyethyl)-phosphate (TBEP) and triphenylphosphate (TPP) and the chlorinated organophosphate esters tris-(2-chloro, 1-methylethyl)-phosphate (TCPP), tris-(2-chloro-, 1-chloromethylethyl)-phosphate (TDCP) and tris-(2-chloroethyl)-phosphate (TCEP). The study showed that there were significant differences in the elimination of chlorinated and non-chlorinated organophosphorous flame retardants. The elimination rates ranged from 57–86% for TiBP, TnBP and TBEP at both STP’s. No elimination of the chlorinated flame retardants TCPP, TDCP and TCEP was observed in any of the sampled STPs. At both STPs the first treatment steps and the final filtration did not contribute to the elimination of the non-chlorinated organophosphorous flame retardants while the aeration step did. At both STPs the efficiency of the cleaning process concerning the flame retardants was comparable. Thus the type of construction of the STP was not relevant for the elimination of these substances. Additionally a strong day-to-day variation was observed, while in one STP a temporal trend for TCPP during the week was found.

Semiclassical Foundation of Universality in Quantum Chaos

Abstract: Fully chaotic dynamics enjoy ergodicity and thus visit everywhere in the accessible space with uniform likeli- hood, over long periods of time. Even long periodic orbits bring about such uniform coverage. Moreover, classical ergodicity provides quantum chaos with universal char- acteristics. Given chaos, quantum energy levels are correlated within local few-level clusters but become statistically in- dependent as their distance grows much larger than the mean level spacing �. The decay of correlations on the scaleis empirically found system independent, within universality classes distinguished by presence or absence of time-reversal (T ) invariance (1, 2). The corresponding universal long-time characteristics act on the Heisenberg scale TH = 2π¯�, withPlanck's constant. Universal spectral fluctuations were conjectured as a manifestation of quantum chaos two decades ago (3). Now, the semiclassical core of a proof can be given. Based on Gutzwiller's periodic-orbit theory (4), our progress comes with two surprises: one lies in its simplicity, the other in the appearance of interesting mathematics (non- trivial properties of permutations). Moreover, the often disputed intimate relation between periodic orbits and quantum field theory is confirmed for good. We thus expect the underlying ideas to radiate beyond spectral fluctuations, like to transport and localization. Technically speaking, we want to show that each com- pletely hyberbolic classical dynamics has a quantum en- ergy spectrum with the same fluctuations as a random- matrix caricature HRMT of its Hamiltonian, even though that caricature has nothing in common with the Hamilto- nian but symmetry (absence or presence of T invariance). The theory of random matrices (RMT) (1, 2, 5), devel- oped by Wigner and Dyson to account for fluctuations in nuclear spectra yields analytic results for correlators of the level density ρ(E), by averaging over suitable ensem- bles of random matrices. Simplest is the two-point corre- lator ρ(E)ρ(E ' ) −ρ(E) ρ(E ' ), where the overlines denote ensemble average. Its Fourier transform with respect to the energy difference E − E ' , called spectral form factor K(τ), is predicted by RMT for systems without time re- versal invariance (unitary class) and with that symmetry (orthogonal class) as

Assessment of Cognitive Load in Multimedia Learning with Dual-Task Methodology: Auditory Load and Modality Effects

Abstract: Using cognitive load theory and cognitivetheory of multimedia learning as a framework,we conducted two within-subject experimentswith 10 participants each in order toinvestigate (1) if the audiovisual presentationof verbal and pictorial learning materialswould lead to a higher demand on phonologicalcognitive capacities than the visual-onlypresentation of the same material, and (2) ifadding seductive background music to anaudiovisual information presentation wouldincrease the phonological cognitive load. Weemployed the dual-task methodology in order toachieve a direct measurement of cognitive loadin the phonological system. In bothexperiments, the modality effect could beconfirmed in the patterns of secondary taskperformance and in the primary learning task.

A review and classification of heuristics for permutation flow-shop scheduling with makespan objective

Abstract: Makespan minimization in permutation flow-shop scheduling is an operations research topic that has been intensively addressed during the last 40 years. Since the problem is known to be NP-hard for ...

Motion control of a tendon-based parallel manipulator using optimal tension distribution

Abstract: This paper presents the motion control of a six degree-of-freedom tendon-based parallel manipulator, which moves a platform with high speed using seven cables. To control the motion of the platform along desired trajectories in space, nonlinear feedforward control laws in the cable length coordinates are used. Taking account of the effect of redundancy on actuation, the optimal tension distribution should be considered to the advantage of the control laws. Using a method based on the analysis of the workspace condition, tension constraints and limiting torque constraints of actuators, an analytical solution for optimum tension distribution was found and used to compute the force in each cable for compensation of dynamic errors. It is experimentally demonstrated that the proposed control laws reduce the energy consumption of the actuators and satisfy the path tracking accuracy.

Oxygen-dependent and tissue-specific regulation of erythropoietin gene expression.

Abstract: Hypoxia-inducible expression of the gene encoding for the glycoprotein hormone erythropoietin (EPO) is the paradigm of oxygen-regulated gene expression. EPO is the main regulator of red blood cell production and more than 100 years of research on the regulation of EPO production have led to the identification of a widespread cellular oxygen sensing mechanism. Central to this signaling cascade is the transcription factor complex hypoxia-inducible factor-1 (HIF-1). Meanwhile, it is known that HIF-1 controls more than 50 oxygen-dependent genes and is now recognized as the main regulator of oxygen homoeostasis in the body. In addition to hypoxic induction, expression of the EPO gene is tightly regulated in a tissue-specific manner. During ontogeny, production of EPO required for erythropoiesis is switched from the fetal liver to the kidneys. Here EPO is mainly synthesized in adulthood. Production of EPO has also been found in organs where it has nonerythropoietic functions: EPO is important for development of the brain and is neuroprotective, whereas it stimulates angiogenesis in the reproductive tract and possibly in other organs. Understanding oxygen and tissue-specific regulation of EPO production is of high relevance for physiology. Moreover, this knowledge might be useful for new therapies to treat human diseases.

Mechanical restriction versus human overreaction triggering congested traffic states.

Abstract: A new cellular automaton traffic model is presented. The focus is on mechanical restrictions of vehicles realized by limited acceleration and deceleration capabilities. These features are incorporated into the model in order to construct the condition of collision-free movement. The strict collision-free criterion imposed by the mechanical restrictions is softened in certain traffic situations, reflecting human overreaction. It is shown that the present model reliably reproduces most empirical findings including synchronized flow, the so-called pinch effect, and the time-headway distribution of free flow. The findings suggest that many free flow phenomena can be attributed to the platoon formation of vehicles (platoon effect).

Discretization effects and the influence of walking speed in cellular automata models for pedestrian dynamics

Abstract: We study discretization effects in cellular automata models for pedestrian dynamics by reducing the cell size. Then a particle occupies more than one cell which leads to subtle effects in the dynamics, e.g. non-local conflict situations. Results from computer simulations of the floor field model are compared with empirical findings. Furthermore, the influence of increasing the maximal walking speed vmax is investigated by increasing the interaction range beyond nearest neighbour interactions. The extension of the model to vmax>1 turns out to be a severe challenge which can be solved in different ways. Four major variants are discussed that take into account different dynamical aspects. The variation of vmax has a strong influence on the shape of the flow–density relation. We show that walking speeds vmax>1 lead to results which are in very good agreement with empirical data.

Gas hydrate single-crystal structure analyses.

Abstract: The first single-crystal diffraction studies on methane, propane, methane/propane, and adamantane gas hydrates SI, SII, and SH have been performed. To circumvent the problem of very slow crystal growth, a novel technique of in situ cocrystallization of gases and liquids resulting in oligocrystalline material in a capillary has been developed. With special data treatment, termed oligo diffractometry, structural data of the gas hydrates of methane, acetylene, propane, a propane/ethanol/methane-mixture and an adamantane/methane-mixture were obtained. Cell parameters are in accord with reported values. Host network and guest are subject to extensive disorder, reducing the reliability of structural information. It was found that most cages are fully occupied by a guest molecule with the exception of the dodecahedral cage in the acetylene hydrate which is only filled to 60%. For adamantane in the icosahedral cage a disordered model is proposed.

Transcription profiling of inner ears from Pou4f3ddl/ddl identifies Gfi1 as a target of the Pou4f3 deafness gene

Abstract: Pou4f3 (Brn3.1, Brn3c) is a class IV POU domain transcription factor that has a central function in the development of all hair cells in the human and mouse inner ear sensory epithelia. A mutation of POU4F3 underlies human autosomal dominant non-syndromic progressive hearing loss DFNA15. Through a comparison of inner ear gene expression profiles of E16.5 wild-type and Pou4f3 mutant deaf mice using a high density oligonucleotide microarray, we identified the gene encoding growth factor independence 1 (Gfi1) as a likely in vivo target gene regulated by Pou4f3. To validate this result, we performed semi-quantitative RT-PCR and in situ hybridizations for Gfi1 on wild-type and Pou4f3 mutant mice. Our results demonstrate that a deficiency of Pou4f3 leads to a statistically significant reduction in Gfi1 expression levels and that the dynamics of Gfi1 mRNA abundance closely follow the pattern of expression for Pou4f3. To examine the role of Gfi1 in the pathogenesis of Pou4f3-related deafness, we performed comparative analyses of the embryonic inner ears of Pou4f3 and Gfi1 mouse mutants using immunohistochemistry and scanning electron microscopy. The loss of Gfi1 results in outer hair cell degeneration, which appears comparable to that observed in Pou4f3 mutants. These results identify Gfi1 as the first downstream target of a hair cell specific transcription factor and suggest that outer hair cell degeneration in Pou4f3 mutants is largely or entirely a result of the loss of expression of Gfi1.

Ceramide, membrane rafts and infections.

Abstract: Distinct domains in the cell membrane, termed rafts, emerge as central for the infection of mammalian cells by many pathogens. Rafts consist of sphingolipids and cholesterol that interact strongly, and thus spontaneously separate from other phospholipids in the cell membrane. Recent studies suggest that at least some pathogens activate the acid sphingomyelinase that releases ceramide in membrane rafts. The generation of ceramide transforms small rafts into a signaling unit and results in the fusion of small rafts to large platforms. Membrane rafts and ceramide-enriched membrane platforms have been shown to mediate internalization of bacteria, viruses and parasites into the host cell, to initiate apoptosis of the host cell upon infection and to regulate the release of cytokines from infected mammalian cells. Furthermore, rafts and ceramide have been implicated in the intracellular trafficking of phagosomes and in the budding of viruses from infected cells. The molecular function of rafts and ceramide-enriched membrane platforms seems to be the re-organization of receptor and intracellular signaling molecules in the cell membrane permitting the interaction of the pathogen with the cell. This suggests that rafts and ceramide-enriched membrane platforms function as central structures involved in the infection of mammalian cells by pathogens and as targets for the development of anti-infective drugs.